Leet (or "1337"), also known as eleet or leetspeak, is an alternative alphabet for the English language that is used primarily on the Internet. It uses various combinations of ASCII characters to replace Latinate letters. For example, leet spellings of the word leet include 1337 and l33t; eleet may be spelled 31337 or 3l33t.
Basically Leet is calculator language! Remember spelling Hello on a calculator? 0.7734